Shutdown problem in SMP system happened on Tegra20

[Bill Huang]

nvpublic
> On Fri, Aug 24, 2012 at 04:23:39PM +0800, Bill Huang wrote:
> > When doing shutdown on Tegra20/Tegra30, we need to read/write PMIC
> > registers through I2C to perform the power off sequence.
> > Unfortunately, sometimes we'll fail to shutdown due to I2C timeout on
> > Tegra20. And the cause of the timeout is due to the CPU which I2C
> > controller IRQ affined to will have chance to be offlined without
> > migrating all irqs affined to it, so the following I2C transactions
> > will fail (no any CPU will handle that interrupt since then).
> 
> > Some snippet of the shutdown codes:
> >
> > void kernel_power_off(void)
> > {
> > 	kernel_shutdown_prepare(SYSTEM_POWER_OFF);
> > 	:
> > 	disable_nonboot_cpus();
> > 	:
> > 	machine_power_off();
> > }
> >
> > void machine_power_off(void)
> > {
> > 	machine_shutdown();
> > 	if (pm_power_off)
> > 		pm_power_off(); /* this is where we send I2C write to shutdown */ }
> >
> > void machine_shutdown(void)
> > {
> > #ifdef CONFIG_SMP
> > 	smp_send_stop();
> > #endif
> > }
> >
> > In "smp_send_stop()", it will send "IPI_CPU_STOPS" to offline other
> > cpus except current cpu (smp_processor_id()), however, current cpu
> > will not always be cpu0 at least at Tegra20, that said for example
> > cpu1 might be the current cpu and cpu0 will be offlined and this is the case why the I2C transaction
> will timeout.
> >
> > For normal case, "disable_nonboot_cpus()" call will disable all other
> > Cpus except cpu0, that means we won't hit the problem mentioned here
> > since cpu0 will always be the current cpu in the call "smp_send_stop", but the call to
> "disable_nonboot_cpus"
> > will happen only when "CONFIG_PM_SLEEP_SMP" is enabled which is not
> > the case for Tegra20/Tegra30, we don't support suspend yet so this can't be enabled.
> 
> So what you're asking for is a feature to do what CONFIG_PM_SLEEP_SMP does, but without
> CONFIG_PM_SLEEP_SMP enabled?

Yeah pretty much, I'm actually asking should we take care of this since maybe not all platforms 
will have this config enabled?
> 
> Why not just ensure that CONFIG_PM_SLEEP_SMP is enabled if your platform requires that the lowest CPU
> number be the CPU dealing with reboot?

Someday we will have it enabled, but before that we'll hit the issue, so you don't think
this should be taken care of? Thanks.